Dialysis machine

ABSTRACT

A disposable cartridge for use in a hemodialysis machine has a blood flowpath for carrying a volume of blood to be treated in a dialyseer and a dialysate flowpath, isolated from the blood flowpath, for delivering a flow of dislysate solution through the dialyser. The cartridge is received in an engine section of the machine. The engine section has first and second platens which close when the cartridge is inserted to retain the cartridge. Actuators and sensors arranged on the second platen control operation of the cartridge.

This application is a continuation of U.S. application Ser. No.11/919,694, filed Oct. 31, 2007, which in turn is a U.S. national stageapplication of International Application No. PCT/GB2006/001668 with anInternational filing date of May 8, 2006 and a priority date of May 6,2005.

FIELD OF THE INVENTION

The present invention relates to dialysis machines and in particular,but not exclusively, to a disposable cartridge for use in hemodialysismachine.

BACKGROUND OF THE INVENTION

Dialysis is a treatment which replaces the renal function of removingexcess fluid and waste products, such as potassium and urea, from blood.The treatment is either employed when renal function has deteriorated toan extent that uremic syndrome becomes a threat to the body's physiology(acute renal failure) or, when a longstanding renal condition impairsthe performance of the kidneys (chronic renal failure).

There are two major types of dialysis, namely hemodialysis andperitoneal dialysis.

In peritoneal dialysis treatment, a dialysate solution is run through atube into the peritoneal cavity. The fluid is left in the cavity for aperiod of time in order to absorb the waste products, and issubsequently removed through the tube for disposal.

It is common for patients in the early stages of treatment for alongstanding renal condition to be treated by peritoneal dialysis beforeprogressing to hemodialysis at a later stage.

In hemodialysis, the patient's blood is removed from the body by anarterial line, is treated by the dialysis machine, and is then returnedto the body by a venous line. The machine passes the blood through adialyser containing tubes formed from a semipermeable membrane. On theexterior of the: semipermeable membrane is a dialysate solution. Thesemipermeable membrane filters the waste products and excess fluid fromthe blood into the dialysate solution. The membrane allows the waste anda controlled volume of fluid to permeate into the dialysate whilstpreventing the loss of larger more desirable molecules, like blood cellsand certain proteins and polypeptides.

The action of dialysis across the membrane is achieved primarily by acombination of diffusion (the migration of molecules by random motionfrom a region of higher concentration to a region of lowerconcentration), and convection (solute movement that results from bulkmovement of solvent,’ usually in response to differences in hydrostaticpressure).

Fluid removal (otherwise known as ultrafiltration) is achieved byaltering the hydrostatic pressure of the dialysate side of the membrane,causing free water to move across the membrane along the pressuregradient.

The correction of uremic acidosis of the blood is achieved by use of abicarbonate buffer. The bicarbonate buffer also allows the correction ofthe blood bicarbonate level.

The dialysis solution consists of a sterilized solution of mineral ions.These ions are contained within an acid buffer which is mixed with theserilised water and bicarbonate base prior to delivery to the dialyser.

Dialysate composition is critical to successful dialysis treatment sincethe level of dialytic exchange across the membrane, and thus thepossibility to restore adequate body electrolytic concentrations andacid-base equilibrium, depends on the composition.

The correct composition is accomplished primarily by formulating adialysate whose constituent concentrations are set to approximate normalvalues in the body.

However, achieving the correct composition of dialysate requires theaccurate control of low volumes of liquid and at present this isachieved by the provision of complex fluid paths, including multiplepumping and valving components on the dialysis machine.

This presents the disadvantage of a complex and costly dialysis machinewhich is at increased risk of failure by virtue of its complexity.Increased maintenance is also a problem since it is essential tominimize machine downtime in order to most efficiently treat thepatient.

A further problem with known hemodialysis machines is that the blood anddialysate solution lines require careful mounting onto the dialysismachine before the treatment can commence. This presents a risk that thelines are not correctly installed, a risk which is particularly relevantto those patients who dialyse at home.

This method of dialysis also presents an increased risk ofcross-infection between patients since the disposable blood anddialysate lines come into contact with the dialysis machine.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a hemodialysissystem which at least mitigates some of the problems described above.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided adisposable cartridge for use in a hemodialysis machine, the cartridgecomprising a blood flowpath for carrying a recirculating volume of bloodto be treated in a dialyser and a dialysate flowpath, isolated from theblood flowpath, for delivering a flow of dialysate solution through thedialyser.

Preferably, the cartridge has a first mixing pump and a second mixingpump, the second mixing pump accepting a homogoneous mix of sterilewater and a first dialysate solution base from the first mixing pump andintroducing a further dialysate solution base.

Preferably, the dialysate pathway includes a first three-way valveupstream of the first dialysate solution mixing pump, the firstthree-way valve controlling delivery of the first dialysate solutionbase into the first mixing pump.

Preferably, the first three-way valve has a mixing pump outlet port, adialysate solution reservoir inlet port and a positive displacement pumpport.

Preferably, the first three-way valve acts to permit a volume of a firstdialysate solution base into the first dialysate solution mixing pump oneach and every stroke of the pump.

Preferably, the dialysate pathway includes a second three-way valveupstream of the second dialysate solution mixing pump.

Preferably, the cartridge includes a dialysate solution reservoir, morepreferably a first reservoir immediately downstream of the first mixingpump and a second reservoir immediately downstream of the second mixingpump.

Preferably, the blood and dialysate fluid pathways pass between a firstoutwardly facing surface of the cartridge and a second outwardly facingsurface of the cartridge.

Preferably, at least some parts of the first and second outwardly facingsurfaces of the cartridge body are covered with a deformable membrane.

Preferably, the valves and pumps on the cartridge are actuable bydeformation of the membrane by the dialysis machine.

Preferably, the blood and dialysate solution fluid pathways are at leastpartially defined by upwardly standing walls projecting outwardly fromthe upper and lower surfaces of the cartridge.

Preferably, the upstanding walls are enclosed by the deformablemembranes.

Preferably, the mixing pumps are membrane pumps.

Preferably, the blood flow path is provided with at least one bloodbubble trap, more preferably, the or each blood bubble trap is providedwith a level sensor.

Preferably, the level sensor is an optical level sensor, or anultrasonic level sensor.

Preferably, the blood bubble trap is provided with an upper and a lowerlevel sensor.

Preferably, the blood bubble trap is provided with a hydrophilicmembrane for removing or adding a volume of air to the blood bubbletrap.

Preferably, the cartridge is provided with a positive displacement pumpplunger acting in combination with the three-way valve to deliver ameasured volume of dialysate solution base into the dialysate solutionmixing pumps.

Preferably, the cartridge is provided with an endotoxin filter,preferably a single use endotoxin filter.

Preferably, the dialysate solution fluid pathway is provided with anultra-sonic flow sensor for detecting the flow rate through thedialysate solution path.

Preferably, the cartridge defines a series of apertures interlinking theportion of fluid pathways defined on the upper surface of the cartridgewith the portion of fluid pathways defined on the lower surface of thecartridge.

According to a second aspect of the invention there is providedadialysis machine adapted to receive the dialysis cartridge of the firstaspect of the invention, the machine including at least one platenarranged in use to hold the cartridge in position on the machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, and withreference to the following drawings, in which:

FIG. 1 is an isometric view of the dialysis machine and cartridge of thecurrent invention,

FIG. 2 is an isometric view of the engine portion of the machine of FIG.1,

FIG. 3 is an isometric view of the cartridge of the present invention,

FIG. 4 is a front view of the cartridge of FIG. 3,

FIG. 5 is a front view of the pumping portion of the cartridge of FIG. 3showing partial hidden detail,

FIG. 6 is a front view of the cartridge of FIG. 3 showing the dialysercover removed,

FIG. 7 is a rear view of the pumping portion of the cartridge of FIG. 3,

FIG. 8 is a top view of the cartridge of FIG. 3,

FIG. 9 is an end view of the cartridge of FIG. 3, and

FIG. 10 is a schematic representation of a dialysate solution basedelivery system according to the present invention.

DETAILED DESCRIPTION

In FIG. 1 a dialysis machine 1 is shown having a cover 2 which opens toreveal a storage compartment 3. The machine has an engine section 4which receives a dialysis cartridge 10.

Referring now to FIG. 2, the engine section 4 is shown in further detailto include first and second platens 5, 6 which dose upon insertion ofthe cartridge 10 into the machine to retain the cartridge in position inuse. The engine 4 has pneumatic actuators 7 and sensors (indicatedgenerally at 8 in FIG. 2) arranged on the second platen to controloperation of the cartridge 10 as will be described in further detailshortly.

In FIGS. 3 and 4 a dialysis cartridge 10 is shown having a pumpingportion 12 (to the right of dashed line I-1 in FIG. 4) and a dialysisportion 14 (to the left of dashed line I-I in FIG. 4). The pumpingportion 12 has the form of a fiat rectangle. The dialysis portion 14 hasa dialyser cover 15 which is shaped so as to contain a dialyser as willbe described in further detail shortly.

Referring briefly to FIG. 8, the pumping portion 12 of the dialysiscartridge 10 has an upper surface 16 and a lower surface 18. The uppersurface 16 and a lower surface 18 are covered by a dear membrane 20, 22,respectively, which is formed from a deformable plastics material. Thefirst and second membrane, 20, 22 are bonded to the upper surface 16 anda lower surface 18, respectively by way of adhesive or similar knownmethod.

Referring now to FIG. 4, the upper surface 16 defines a series ofupstanding walls indicated, for example, as 24. The upstanding walls 24define a system of flow channels as will be described in further detailshortly. The channels are enclosed at the outermost part of the uppersurface 16, by the first membrane 20. Accordingly, the upper surface 16defines a series of fluid channels for carrying either the blood to bedialysed, or the Dialysate solution.

The cartridge 10 also defines the series of apertures, indicatedgenerally for example at 26 in FIG. 4. These apertures provide a fluidpathway through the cartridge 10, the purpose of which will now bedescribed.

Referring to FIG. 7, the lower surface 18 also defines a series ofupstanding walls 24, which collectively define a labyrinth of fluidchannels enclosed by the second membrane 22.

In combination therefore the upper surface 16, lower surface 18 and thefirst and second membranes 20, 22 form a series of interconnected fluidflow paths on both sides of the pumping portion 12. This labyrinth offluid flowing pathways will now be described in further detail.

The first membrane 20 is bonded to the upper surface 16, and similarlythe second membrane 22 bonded to the lower surface 18, so as to containthe fluids within their respective channels.

The dialyser cartridge 10 defines two primary fluid pathways, firstly, aflow path for blood and secondly a flow path for the dialysate solution.The blood pathway is formed as follows.

The patient's blood enters the dialysis cartridge 10 via an arterialport 28. The blood then passes from the upper surface 16 to the lowersurface 18 via an arterial port aperture 30 where it is then carried byan arterial port channel 32 from the arterial aperture 30 to an arterialblood bubble trap 34. The arterial blood bubble trap 34 has an inlet lip36 for directing the incoming blood towards the bottom of the trap.Arranged at the bottom of the trap is a blood bubble trap exit 38 whichcarries the blood from the arterial blood bubble trap 34 to an arterialblood bubble trap aperture 40 via channel 42.

The purpose of the arterial blood bubble trap 34 is to remove from thearterial blood supply any gas bubbles which may be contained therein.Gas bubbles may impair the performance of dialyser, and furthermore,present a risk to the patient if they were reintroduced back into thebody via the venous blood line. The blood bubble trap 34 is alsoprovided with an upper level sensor port 44 and a lower level sensorport 46. The level sensor ports 44, 46 are arranged to coincide withcorresponding optical level sensors arranged on the dialysis machine.Accordingly, the level sensors are able to optically interrogate thearterial blood bubble trap 34 so as to ensure that the level in theblood bubble trap is above the level of the lower level sensor port 46and below the level of the upper level sensor port 44. It is importantto ensure that the blood level remains between these two levels so thatthere always remains a volume of air in the blood level trap into whichany gas bubbles carried in the blood can migrate.

Having passed through the arterial blood bubble trap aperture 40 theblood is carried on the upper surface 16 to a blood pump inlet valve 48(see FIG. 4).

Referring to FIG. 4, the blood pump inlet valve 48 is operable between aclosed condition and an open condition as follows. The valve 48 has anouter annular upstanding wall 50 and an inner annular upstanding wall52. Arranged inwardly of the inner upstanding annular wall 52 is a valveaperture 54. The inner upstanding annular wall 52 is recessed from theouter upstanding annual wall 50 in a direction towards the cartridge 10.Arranged between the inner and outer upstanding annual wall 50, 52 is asector aperture 56 which acts as an outlet from the valve 48.Accordingly, the valve 48 has a valve inlet in the form of valveaperture 54 and an outlet in the form of the sector aperture 56. Asdiscussed previously, the lower surface 18 has its outer service coveredby a deformable membrane 22. The deformable membrane 22 rests againstthe outwardly facing surface of the outer upstanding annular wall 50where the valve is in the un-actuated, open state. In order to changethe condition of the valve 48 from the open state to the closed state,the dialysis machine applies a positive pressure to the exterior surfaceof the second membrane 22 in order to drive the inner surface of themembrane on to the outwardly facing surface of the inner upstandingannular wall 50. This doses the inlet to the valve thereby preventingflow through the valve.

With the blood pump inlet valve 48 in the open state, the blood flowsthrough the arterial blood bubble trap aperture 40 over the innerupwardly standing wall 50 and through the sector aperture 56 so as toexit the blood pump inlet valve 48. From the sector aperture 56 theblood then flows down a blood pump inlet channel 58 and into a bloodpump 60 via a blood pump inlet 62.

The blood pump is defined by a dome shaped pump cavity 64 into which theblood pump inlet 62 opens. Arranged at the centre of the pump chamber 64is a pump outlet 66. The outer edge of the pump chamber 64 is defiled byan annular upstanding wall 68, the outwardly facing surface of which isin contact with the inner surface of the second membrane 22. A volume ofblood is drawn into the pump chamber 64, through the open blood pumpinlet valve 48 as follows.

The dialysis machine generates a negative pressure on the outsidesurface of the second membrane 22 in order to deform the membraneoutwardly away from the lower surface 18. With the pump chamber 64 full,and the pump at full stroke, the blood pump inlet valve 48 is closed bythe dialysis machine generating positive pressure on the outside surfaceof the second membrane 22 in order to dose the valve aperture 54. Thepump chamber 64 is then evacuated by the dialysis machine applying apositive pressure to the outside surface of the second membrane 22 inorder to drive the blood contained within the pump chamber 64 throughthe pump outlet 66. The pump outlet 66 is in fluid communication with ablood pump outlet valve 70 which is identical in form to the blood pumpinlet valve 48. It follows that with the blood pump inlet valve closed,and the blood pump 60 being driven by the dialysis machine to evacuatethe pump 64, the blood pump outlet valve 70 is in an open state in orderto permit the flow of blood past the valve 70 and through a blood pumpoutlet valve aperture 72.

Accordingly, the blood pump 60 is in combination with the blood pumpinlet valve 48 and the blood pump outlet valve 70. Specifically, theblood pump inlet valve 48 opens when the blood pump is in the expansionstroke in order to admit blood into the pump chamber, whilst the bloodpump outlet valve 70 remains closed in order to prevent back-flow ofblood through the system. The inlet valve 48 then closes at the sametime as the outlet valve 70 is opened in order to allow the compressionstroke of the flow pump to drive the blood from the pump chamber 64 andthrough the blood pump outlet valve aperture 72.

From the aperture 72, the blood then flows through a pressure sensorchamber 74. As the blood flows through the chamber 74, the fluidpressure causes a force to be applied to the first membrane 20 which inturn causes a deflection in the membrane. This deflection is detected bya sensor provided in the dialysis machine and this measured deflectionis calibrated to generate a blood pressure reading for within thecartridge.

From the pressure sensor chamber 74 the blood then passes through adialyser blood port 76.

Referring now to FIG. 6, the blood flows from the dialyser blood port 66down a dialyser blood line 78 and into the bottom end of a dialyser 80of known design. The dialyser 80 contains multiple axially extendingsemi-permeable tubes through which the blood passes. Upon exiting thedialyser 80 the blood travels down a dialyser return blood line 82before passing into a venous blood bubble trap 86 via a dialyser bloodreturn Port 84.

The venous blood bubble trap 86 is similar in design to the arterialblood bubble trap 34 in that it has an inlet lip 88, an optical levelsensor 90 and a hydrophilic membrane 94 to allow the hydrolysis machinewithdraw or administer a volume of air to or from the bubble trap inorder to maintain a constant blood level within the bubble trap. Thevenous blood level trap 86 is further provided with an ultrasonic levelsensor 92 the design of which will be described in further detailshortly. At the bottom end of the valve trap is a thrombus filter 96 fortrapping blood dots within the bubble trap. The Thrombus filter may beof conical form as in known thrombus filters or may be wedge shaped.Having passed through the thrombus filter 96, the blood passes throughan ultrasonic flow rate sensor 98 which will be described in furtherdetail shortly. The blood is then returned to the patient via a venousport 100.

The blood therefore completes its passage through the dialysis cartridge10 from the arterial port 28 through the arterial blood bubble trap 34,the blood pump inlet valve 48 and into the blood pump 60. From bloodpump 60 the blood is driven past the blood pump outlet valve 70 and intothe dialyser 80 via the cross membrane pressure sensor 74. Upon exitfrom the dialyser 80, the blood is returned to the dialysis cartridge 10via the dialyser blood return port 84. Upon exit from the port 84 theblood enters the venous blood bubble trap 86, passes through thethrombus filter 96 and flow sensor 98 before being returned to thepatient via the venous port 100.

A syringe 71 is provided which introduces a volume of an anti-coagulantdrug such as heparin into the blood line between the blood pump outletvalve 70 and the dialyser 80. The syringe plunger 73 is driven by themachine engine as shown in FIG. 2.

As described above, dialysis occurs across a semi-permeable membrane, inthis instance the semi-permeable tubes provided within the dialyser 80.As described, the blood flows through the centre of the semi-permeabletubes and it therefore follow that the dialysate solution flows in thespace within the dialyser 80 between the tubes. The mixing of thedialysate solution on the cartridge at the correct concentration willnow be described in detail.

The pump portion 12 defines the dialysate flow path in addition to theblood flow path as described above.

Accordingly, the dialysis cartridge 10 provides for the mixing into asterile water supply of a small volume of concentrated bicarbonatesolution and a small volume of acid solution. The resulting dialysatesolution is pumped from the pumping portion to deliver the solution tothe dialyser. The cartridge further allows for the accurate sensing ofdialysate solution concentration, dialysate flow rate and dialysatepressure.

Sterile water enters the dialysis cartridge 10 via a sterile water inlet102. The sterile water is then mixed with a controlled volume ofbicarbonate solution base as follows. The cartridge 10 defines a chamber104, for receiving the plunger of a positive displacement pump (notshown for clarity in FIGS. 3 to 9). The pump acts in combination with athree-way valve 106 of known design. The pump and three-way valve 106are operated by the dialysis machine to micro-dose a controlled volumeof bicarbonate solution into a bicarbonate pump 108. The bicarbonatepump 108 is of similar design to the blood pump 60 with the exceptionthat the bicarbonate pump 108 is additionally provided with an inlet 110from the three-way valve 106. The bicarbonate pump 108 is controlled inexactly the same manner to the flow pump 60 in order to draw a volume ofsterile water through the sterile port at 102 and past a bicarbonateinlet pump 112 whilst a bicarbonate pump outlet valve 114 remainsclosed. At the same time as a volume of sterile water is drawn into thepump a small volume of saturated bicarbonate solution is injected intothe bicarbonate pump 108 by a positive displacement pump. The body ofthe positive displacement pump is defined by the cartridge body. Thesaturated bicarbonate solution is drawn from a reservoir on the dialysismachine. The solution is delivered to the pump via a bicarbonate inletchannel 105 and three-way valve 106.

The action of drawing the water into the pump chamber by means ofapplying a negative pressure to the outer surface of the first membrane20 generates a turbulent flow within the pump chamber which causes thesterile water and bicarbonate solution to be mixed thoroughly within thepump chamber. Accordingly, at the point where the bicarbonate pump inletvalve 112 is closed, and the outlet valve 114 opens in order to drive asolution from the pump chamber, a thorough homogoneous mixing has beenachieved.

The bicarbonate and water solution is pumped out of the pump chamber viaa pump exit 116 from which it flows past the pump outlet valve 114 andinto a water-bicarbonate solution reservoir 118. The volume of thewater-bicarbonate reservoir 118 is approximately four times the volumeof the bicarbonate pump chamber and performs two functions. Firstly, itfurther ensures that the mixture is homogenous, and secondly acts as afluid buffer within the dialysate solution flow path, the purpose ofwhich will be described in further detail shortly.

The bicarbonate solution reservoir 118 is provided with a conductivitysensing probe 120 and a temperature sensing probe 122, an upper levelsensor 124 and a lower level sensor 126.

The conductivity and temperature sensor probes are provided to contactwith conductivity and temperature sensors in the dialysis machine. Themeasurements are used to deduce the concentration of thewater-bicarbonate solution in the reservoir 118. The resevoir also actsas buffer to allow for the various system pumps being out of phase.Accordingly, the level in the resevoir is able to rise and fall therebyaveraging out pressure spikes in the system.

From the water-bicarbonate resevoir 118, the solution is drawn into anacid pump 128 past an open acid pump inlet valve 130. Coupled to theacid pump 128 is an acid pump outlet valve 132. The purpose of the acidpump 128 is to introduce a small volume of acid solution base into thewater-bicarbonate solution. This process is achieved using the samevaluing and pumping methodology as employed for the bicarbonate pump108. Specifically, a second chamber 107 is provided for receiving theplunger of a second positive displacement pump. A volume of acidsolution base is thereby dispensed down a acid inlet channel 109 to asecond 3-way valve 111. Under the action of the pump 128,water-bicarbonate solution is drawn into the pump chamber. The the acidsolution base is injected into the pump by a second positivedisplacement pump. The fluids are thoroughly mixed in the turbulent flowwithin the pump chamber before being dispensed passed the outlet valve132 into a water-bicarbonate-acid reservoir 138.

The water-bicarbonate-acid reservoir 138 is provided with a conductivitysensing probe 144 and a temperature sensing probe 146, an upper levelsensor 140 and a lower level sensor 142, in common with thewater-bicarbonate reservoir 118.

From the water-bicarbonate-acid reservoir 138, the solution flowsthrough a resevoir exit 147 (see FIG. 7) into a flow balance inletchannel 148. The solution is thereby delivered to the flow balancer 150.

The purpose of the flow balancer 150 is to ensure that the volume ofdialysate solution pumped into the dialyser is the same as thatwithdrawn from the dialyser 80. The purpose of matching the flow intoand out of the dialyser is to match the osmotic potential of thedialysate solution within the dialyser to the osmotic potential of theblood. This ensures that the volume of the fluid removed from the blood,or transferred to the blood, can be carefully controlled. This iscritical to ensuring that the patient is not hydrated or dehydrated to adangerous extent during the dialysis treatment.

The flow balancer 150 is provided with a first flow balance pump 152 anda second flow balance pump 154. The first and second flow balance pumps152,154 have a similar mode of operation to the blood pump 60, and themixing pumps 108, 128. However, the flow path for delivering fluid toeach of the flow balance pumps 152, 154 is rather more complex due tothe way in which the flow balancer 150 achieves the controlled fluidflow input and output from the dialyser 80.

In principal, the flow balancer 150 operates by using the first flowbalance pump 152 to pump dialysate solution into the dialyser, and thesecond flow balance pump 154 to withdraw the dialysate solution from thedialyser, for a period of time, before switching the second flow balancepump 154 to pump dialysate solution into the dialyser, and the firstflow balance pump 152 withdrawing dialysate solution from the dialyser.The purpose of this mode of operation is to eliminate the effect ofmanufacturing tolerances in generating a mismatch in the volume of thepump chamber in each of the flow balance pumps 152, 154. For example,were the first flow balance pump 152 used permanently to pump dialysatesolution into the dialyser, and the second flow balance pump 154 used towithdraw dialysate solution from the dialyser, then over a period oftime even the very small discrepency in the pump chamber volume of thepumps would lead to a dangerous imbalance in the volume of dialysatesolution being pumped into, and withdrawn from, the dialyser.

By switching the first and second flow balance pumps 152,154, any errorsin the chamber volume are averaged over time, thereby ensuring a balancein the flow across the dialyser.

In selective fluid communication with the first flow balance pump 152are a first flow balance pump first inlet valve 156, a first flowbalance pump second inlet valve 158, a first flow balance pump firstoutlet valve 160 and a first flow balance pump second outlet valve 162.Similarly, in selectable fluid communication with the second flowbalance pump 154 are a second flow balance pump first inlet valve 164, asecond flow balance pump second inlet valve 166, a second flow balancepump first outlet valve 168 and a second flow balance pump second outletvalve 170.

The first mode of operation of the flow balancer 150 will now bedescribed in detail. In the first mode of operation, the first flowbalance pump first inlet valve 156, first flow balance pump secondoutlet valve 162, second flow balance pump second inlet valve 166 andsecond flow balance pump first outlet valve 168 are all held in theclosed position by the dialysis machine applying a positive pressure tothe outside surface of the first membrane 20 in the region of each ofthe valves. Accordingly, the first mode of operation the second flowbalance pump 154 is operated to pump dialysate solution into thedialyser, and the first flow balance pump 152 is operated to withdrawdialysate solution from the dialyser.

With the first flow balance pump first inlet valve 156 in the closedposition, dialysate solution passing out of the bicarbonate acidreservoir 138 flows past the first flow balance pump first inlet valve156 along a flow balance inlet channel 148. The dialysate solution thenpasses from the lower surface 18 to upper surface 16 via an aperture172. With the second flow balance pump first inlet valve 164 in its openposition, the second flow balance pump 154 is able to draw a volume ofdialysate solution into the pump chamber under the action of thedialysis machine generating a negative pressure on the outward facingsurface of the first membrane 20.

As soon as the second flow balance pump 154 is at full capacity, thesecond flow balance pump first inlet valve 164 is closed, and the secondflow balance pump second outlet valve 170 is opened. The pump 154 isthen actuated to discharge the dialysate solution through an aperture174 and the dialysate solution then flows along channel 176 as shown inFIG. 10. The dialysate solution then passes through an endotoxin filter178 before passing through a dialyser output port 180 via channel 182.

Referring now to FIG. 6, from the dialysate outlet port 180, dialysatesolution passes along a dialysate inlet pipe 180 before passing alongthe dialyser 80 from top to bottom as shown in FIG. 9. In order toreturn the dialysate solution from the dialyser 80 to the pumpingportion 12, a dialysate outlet pipe 184 carries dialysate solution to adialysate inlet port 186. Upon return to the pumping portion 12, thedialysate solution passes through a colour sensor portion 188 in orderto allow a colour sensor arranged on the dialysis machine to interrogatethe dialysate solution to detect for blood leakage into the dialysatesolution within the dialyser 80. On exit from the colour sensor portion188, the dialysate solution passes through aperture 190 and from thereinto a flow balance return channel 192.

Since the second flow balance pump second inlet valve 166 is closed, thedialysate solution flows past aperture 194 towards the first flowbalance pump second inlet valve 158. With the valve 158 in the openposition, the first flow balance pump 152 is able to draw in to the pumpchamber a volume of dialysate solution through the inlet valve 158 underthe action of a positive pressure generating by the dialysis machine onthe outwardly facing surface of the-first membrane 20. The first flowbalance pump second inlet valve 158 then doses, the first flow balancepump first outlet valve 160 opens, and the pump 152 drives the dialysatesolution from the fluid chamber through the outlet valve 160. The outletvalve 160 is then closed, the inlet valve 158 opened and the pump 152driven to draw in a further volume of dialysate solution ready fordispensing in the next pump cycle.

Having been delivered past the outlet valve 160, the dialysate solutionflows through aperture 196 since the second flow balance pump firstoutlet valve 168 is closed during the mode of operation. The dialysatesolution then passes through an ultrasonic flow sensor 198 which will bedescribed in further detail shortly, before exiting the dialysiscartridge 10 by way of dialysate solution drain 200.

In the second mode of operation, the roles of the first and second flowbalance pumps 152, 154 are reversed. In other words, the first flowbalance pump second inlet valve 158 and first flow balance pump firstoutlet valve 160 are held closed whilst the first inlet valve 156 andsecond outlet valve 162 are operated to control the flow of Dialysatesolution into and out for the valve chamber. Similarly, with referenceto the second flow balance pump 154, the second flow balance pump firstinlet valve 164 and second flow balance pump second outlet valve 170 areheld in a closed position whilst the second flow balance pump secondinlet valve 166 and second flow balance pump and first outlet valve 168are operated to control the flow of the acid solution into and out ofthe pump chamber.

The technique of flow balancing, as described above, is provided toensure that exactly the same volume of dialysate solution is pumped intothe dialyser 80 as is removed from it. However, in certain dialysistreatments there is a requirement to either remove excess fluid from theblood, or to transfer fluid back into the blood. This is achieved by theprocess of ultra-filtration in which the flow balance circuit is placedslightly out of balance by either introducing or removing a small volumeof liquid to or from the diayslate solution. In the dialysis cartridgeof the present invention this is achieved by an ultra-filtrationthree-way valve 206 which acts in combination with a positivedisplacement pump received in chamber 208 on the cartridge. Thiscombination of three-way valve and positive displacement pump isidentical to that used to introduce the bicarbonate solution into thebicarbonate pump 108. The positive displacement pump plunger is receivedwithin the chamber 208 and is positioned by a drive, for example astepper motor, on the dialysis machine.

The cartridge 10 has a drainage channel 202 for draining excess fluidfrom the water-bicarbonate reservoir 118 and the water-bicarbonate-acidreservoir 138. The drainage channel carries excess fluid from thereservoirs 118, 138 and dumps the fluid to drain via a drainage port 204which is in fluid communication with a drainage port in the dialysismachine.

Accordingly, the dialysis cartridge 10 provides two distinct flow paths,firstly for blood, and secondly for dialysate solution. The provision ofan upper surface 16 and a lower surface 18, with apertures therebetweenallows the transfer of fluid from the outwardly facing surface of theupper surface to be on the facing surface of the lower surface. Theblood flow path and the dialysate solution flow path are maintaineddiscrete from one another by upstanding walls extending from the uppersurface and lower surface. The outer surface of the upstanding wallsabuts a deformable membrane in order to seal the flow path.

It will be appreciated that the apertures provided in the first andsecond cartridge bodies 16, 18 allow for the most convenient packagingof the various cartridge features. It is dear that this feature providesa distinct advantage over cartridges which define all of the flowchannels on only one side of the cartridge.

In an alternative embodiment of cartridge, the arterial blood bubbletrap 34 and venous blood bubble trap 86 have a collapsible element inthe form of a concertina section of plastic material so as to limit thearea of blood/air interface. This is particularly advantageous in thatthe reduced blood/air interface reduces the risk of clotting and/orseparation of the blood.

A further alternative feature of the bubble trap is to replace thehydrophilic membrane 94 with a membrane pump similar to the blood pump60. Accordingly, instead of air being added or removed to the bubbletrap by way of the transfer of air across the hydrophilic membrane, thetransfer of air can be achieved by the displacement of the membrane bythe application of either a positive or negative pressure on theoutwardly facing surface of the membrane. Furthermore, the extent ofactuation of the membrane could be monitored in order to detect where anexcessive volume of air is either being added to the reservoir orremoved from the reservoir.

In a further alternative embodiment, each of the valves, for example 48,106, 112, 114, 164 etc are provided with rigid disks which have thediameter equal to or slightly greater than the diameter of the innerupwardly standing wall. The rigid disk is arranged between the innerupwardly standing wall and the membrane. The purpose of the rigid discis to minimise the deformation required in the membrane in order to sealthe valve. In other words, the membrane acts on the rigid disc which inturn forms a valve seat on the inner upwardly standing wall. The resultof the reduced deformation of the membrane is that the transient shockwaves generated in the valve by virtue of the switching between open andclosed is reduced since the valve is closed at a lower peak pressurethan would be necessary if the rigid disc were not present. A furtherbenefit in addition to the reduction in pressure spiking observed in thevalve body is the reduced blood damage achieved by smoother operation ofthe valve between its open and closed state.

Referring now to FIG. 10, the positive displacement pump and three-wayvalve on the current invention are shown schematically in furtherdetail. The three-way valve is indicated generally at 106. It will beappreciated that the three-way valve 106 is identical to the valve incommunication with the pump 128 and the ultra-filtration valve 206. Thedetailed description of three-way valve 106 therefore applies equally tothe other two three-way valves provided on the dialysis cartridge.

The bicarbonate mixing pump 108 is connected via a fluid line to anoutput 250 of the three-way valve 106. The three-way valve also has areservoir inlet 252 and a pump inlet 254. The reservoir inlet 252 isconnected to a bicarbonate solution reservoir 255. The reservoir 255 isprovided on the dialysis machine, or attached thereto, and does not formpart of the cartridge itself. The positive displacement pump isindicated generally at 258. The positive displacement pump includes apneumatic cylinder 260 which drives a piston arm 262 in a reciprocatingmanner. At the opposite end of the piston arm to the piston cylinder isa plunger 264 which acts within the cartridge chamber 104 (see FIG. 10).

On the return stroke indicated at A in FIG. 10, the plunger 264 is movedwithin the chamber 104 to draw in to the chamber a measured volume ofdialysate solution from the bicarbonate solution reservoir 255. Thistransfer of fluid is achieved by the closure of the three-way valveoutput 250, with the reservoir inlet and pump inlet 252, 254 remainingopen. The piston arm 262 is withdrawn in direction A until an abutment268 provided on the piston arm 262 comes into contact with a moveableend stop 270.

Upon the abutment 268 hitting the moveable end stop 270, the pneumaticcylinder 268 is driven in direction B in order to dispense the dialysatesolution from the chamber 104 into the bicarbonate mixing pump 108. Thistransfer of fluids is achieved by the closure of the reservoir inlet252, and the opening of the three-way valve output 250. The pneumaticcylinder 260 drives the piston ring 264 in direction B until the pistonring abuts the extreme left hand end of the chamber 104. Accordingly, byreciprocating the movement of the cylinder piston arm 262 in a knownmanner, a quantity of bicarbonate solution is repeatedly dispensed intothe bicarbonate mixing pump 108. Furthermore, by adjusting the positionof the removable end stop 270, the volume of fluid dispensed can beaccurately set. The moveable end stop 270 is positioned by a steppermotor or similar accurate positioning drive system.

The advantage of this system is that the pneumatic cylinder 260 providesthe speed of the reciprocating movement required to deliver discretevolumes of fluid into the mixing pump 108 at the required rate. Astepper motor which is extremely accurate but not able to provide thespeed reciprocation required, is therefore only used to set the dispensevolume of fluid by positioning the moveable end-stop accurately.

It will be appreciated that the bicarbonate mixing pump 108, three-wayvalve 106, and chamber 104 are provided on the cartridge. However, theremainder of the components described in respect of FIG. 10 is providedon the dialysis machine. Importantly therefore, the pneumatic cylinder,stepper motor and moveable lens stop are provided on the machine, notthe cartridge.

It will be appreciated that the cartridge of the current inventionprovides the significant advantage of delivering a homogenous mix ofdialysis solution on each and every stroke of the first and second flowbalance pumps 152, 154. This feature is critical to delivering a stabledialysis treatment. Furthermore, all of the fluid pathways, pumps andvalves required to achieve a homogenous mix are arranged on thecartridge itself. This provides significant advantage since thecartridge contains all of the fluid pathways.

It is conceivable within the scope of the invention that where theprovision of a membrane is not necessary to contain flow within achannel, it is conceivable within the scope of invention that such asection of membrane could be removed from the dialysis cartridge 10following the application of the membrane sheet on to the outwardlyfacing surface of the cartridge.

Additionally, it is conceivable within the scope of invention thatcertain sections of flow channel may be strengthened for example, by thethickening of the upwardly standing walls, in order to reduce anyflexing in the flow channels resulting from the varied hydrostaticpressure in the fluids.

1-30. (canceled)
 31. A disposable cartridge for use in a hemodialysismachine, the cartridge comprising a blood flowpath for carrying a volumeof blood to be treated in a dialyser and a dialysate flowpath, isolatedfrom the blood flowpath, for delivering a flow of dialysate solutionthrough the dialyser.
 32. The disposable cartridge of claim 31, whereinin use the dialysate flowpath forms part of a recirculating dialysateloop including the dialyser and a regenerative filter.
 33. Thedisposable cartridge of claim 31, wherein in use the dialysate flowpathforms part of a continuous dialysate line including a sterile watersupply inlet from the hemodialysis machine, the dialyser and a wastefluid outlet, said waste fluid outlet downstream of the dialyser. 34.The disposable cartridge of claim 33, wherein the cartridge includes thedialyser or is adapted to be attachable to the dialyser.
 35. Thedisposable cartridge of claim 33, wherein the cartridge fully enclosesthe blood flowpath and the dialysate flowpath.
 36. The disposablecartridge of claim 33, wherein the cartridge comprises a rigid body. 37.The disposable cartridge of claim 36, wherein the rigid body has a firstoutwardly facing surface and a second outwardly facing surface, each ofthe outwardly facing surfaces being enclosed by a deformable membrane.38. The disposable cartridge of claim 37, wherein the first and secondoutwardly facing surfaces collectively define a blood flow channel and adialysate flow channel, the deformable membranes enclosing the flowchannels to form the blood flowpath and the dialysate flowpath.
 39. Thedisposable cartridge of claim 38, wherein at least part of the bloodflowpath is formed on each of the first and second outwardly facingsurfaces.
 40. The disposable cartridge of claim 39, wherein at leastpart of the dialysate flowpath is formed on each of the first and secondoutwardly facing surfaces.
 41. The disposable cartridge of of claim 37,wherein, in use, the rigid body is held in place in the hemodialysismachine by at least one moveable platen which engages one of the firstor second outwardly facing surfaces.
 42. The disposable cartridge claim41, wherein the dialysate flow path includes a sterile water inlet toadmit sterile water onto the cartridge from the hemodialysis machine.43. The disposable cartridge of claim 42, wherein the dialysate flowpath includes a first mixing pump having a pump chamber for receiving apredetermined volume of sterile water, and a dispenser for dispensinginto the pump chamber a predetermined volume of a first dialysatesolution base, the first mixing pump operable to form and pump theresulting homogeneous mixture of sterile water and first dialysatesolution base out of the pump chamber.
 44. The disposable cartridge ofclaim 43, wherein the dialysate flow path includes a second mixing pumpdownstream of the first mixing pump, the second mixing pump having asecond pump chamber for receiving a predetermined volume of the mix ofsterile water and first dialysate solution base from the first mixingpump, the dialysate flow path further including a dispenser fordispensing into the second pump chamber a predetermined volume of asecond dialysate solution base, the second mixing pump operable to pumpthe resulting dialysate solution of sterile water and first and seconddialysate solution bases out of the second pump chamber.
 45. Thedisposable cartridge of claim 43, wherein the first dialysate solutionbase is a bicarbonate solution.
 46. The disposable cartridge of claim44, wherein the second dialysate solution base is one of an acid andacetate solution.
 47. The disposable cartridge of claim 44, wherein theoperation of each of the first and second mixing pumps is achieved bydisplacement of the deformable membrane by way of pneumatic actuation.48. The disposable cartridge of claim 43, wherein operation of the firstmixing pump is such that the predetermined volume of first dialysatesolution base is delivered into the pump chamber at the same time as thepump is actuated to draw into the pump chamber a volume of sterile watersuch that every stroke of the pump delivers a homogoneous mix of sterilewater and first dialysate solution base.
 49. The disposable cartridge ofclaim 44, wherein operation of the second mixing pump is such that thepredetermined volume of the second dialysate solution base is deliveredinto the pump chamber at the same time as the pump is actuated to drawinto the pump chamber a volume of homogoneous mix of sterile water andfirst dialysate solution base such that every stroke of the secondmixing pump delivers a homogoneous dialysate solution.
 50. Thedisposable cartridge of claim 31, wherein the cartridge includes a flowbalancer for achieving a balance of dialysate solution flow volumeobserved at the dialyser inlet and at the dialyser outlet outlet overthe course of a treatment.
 51. The disposable cartridge of claim 50,wherein the flow balancer comprises a first flow balance pump and asecond flow balance pump, the balance pumps operable between two modesof operation, a first mode of operation in which the first flow balancepump is arranged in a dialysate line, said first flow balance pumpdownstream of the first and second mixing pumps and upstream of thedialyser and the second flow balance pump is arranged in said dialysateline, said second flow balance pump downstream of the dialyser, and asecond mode of operation in which the second flow balance pump isarranged in the dialysate line, said second flow balance pump downstreamof the first and second mixing pumps and upstream of the dialyser andthe first flow balance pump is arranged in the dialysate line, saidfirst flow balance pump downstream of the dialyser.
 52. The disposablecartridge of claim 43, wherein the cartridge includes a delivery pumpfor delivering heparin into the blood flowpath.
 53. A hemodialysismachine adapted to receive the dialysis cartridge of claim 31, themachine including at least one platen arranged in use to hold thecartridge in position on the machine.
 54. The hemodialysis machine ofclaim 53, wherein the at least one platen includes one or more levelsensors arranged to sense the level of fluid on the cartridge.
 55. Thehemodialysis machine of claim 53, wherein the at least one platenincludes one or more pressure sensors arranged to sense the fluidpressure on the cartridge.
 56. The hemodialysis machine of claim 53,wherein the at least one platen includes one or more flow sensorsarranged to sense the flow rate of one or more fluids on the cartridge.57. The hemodialysis machine of claim 53, wherein the at least oneplaten includes one or more colour sensors arranged to detect bloodleaks on the cartridge.
 58. The hemodialysis machine of claim 53,wherein the at least one platen includes one or more conductivitysensors, each sensor arranged to measure the concentration of thedialysate solution within the cartridge.
 59. The hemodialysis machine ofclaim 53, wherein the machine comprises a pair of platens which cometogether in use to hold the cartridge in position.